1. Field of the Invention
This invention relates generally to the fabrication of semiconductor devices and, more particularly, to an improved contact structure for semiconductor devices which can withstand the high-temperature processes necessary at later stages of device fabrication flow.
2. Description of the Related Art
As the density of integrated devices in dynamic random access memory (DRAM) devices has increased, the size of the contact hole has decreased while the aspect ratio of the contact hole has increased. As a result, the fabrication of contact structures for sub-micron complementary metal oxide semiconductor (CMOS) devices is difficult. Typically, a contact structure is formed after the formation of the capacitor elements. However, if the contact structure can be formed before the formation of the capacitor structure and withstand the high temperature steps required in the formation of the capacitor structure(s), the process flow can be simplified and a reduced aspect ratio for the contact hole(s) can be obtained. In the prior art, a TiN diffusion barrier between the tungsten conducting layer and the substrate is formed by sputtering titanium in an ambient environment which includes nitrogen or by chemical vapor deposition. The Ti/TiN materials can not withstand a high temperature cycle at temperatures required for the formation of a capacitor structure.
A need has been felt for a technique for forming a contact with a diffusion barrier which is easy to fabricate and which has sufficient thermal stability to withstand the process temperature required in the formation of contact structures.